I installed VSTS build agent on mac to build xamarin iOS project. Builds worked fine until I added powershell build step. Even though I installed powershell for mac (https://git
If you're sure that DotNetFramework is installed then you can go to the Agent Queues settings and add a custom Capability to it called exactly that.
That should allow it to run but it might fail after that if the agent can't actually find them, but it might also succeed so it's probably worth a try.